1. Field of the Invention
The present invention relates to an apparatus for cutting off a thread chain formed consecutively with the tail end of a seam on a fabric, and for sewing the cut thread chain connected to the needle into the seam of the initial end of the fabric to be sewn next, thereby preventing looseness (ravel) of the thread at the beginning end of sewing.
2. Description of the Invention
Conventionally, such device as disclosed in Japanese Publication No. Sho 56-50599 of examined application (corresponding U.S. Pat. No. 4,038,933) is known for retaining a thread chain in an overlock sewing machine. The conventional device for retaining a thread chain manages a thread chain in the following manner. A thread chain formed consecutively with stitches in a margin of fabric is drawn into a suction tube by air suction in a back side of a needle location, and cut by a cutting device provided in an opening of the tube. Thereafter, a free end of the thread chain remaining in a side of a sewing machine after the cutting operation is drawn into an internal bore of tongue by a suction force of air flowing into the tongue. Then, when a sewing operation is restarted, and a next workpiece is fed in the predetermined direction, the thread chain drawn into the internal bore of tongue is pulled out of the tongue, and sewn into seam formed in the fabric. In such manner, ravel of the thread at the commencement of stitching in a workpiece is prevented without a special bar tacking process.
In such conventional device for retaining a thread chain as described above, a length of thread chain remaining in a side of a sewing machine after the cutting operation is uneven, and it is difficult to draw a free end of the thread chain securely into an internal bore of tongue. Even if a free end of thread chain remaining in a side of a sewing machine is drawn into an internal bore of tongue, it has been a problem that a length of thread chain sewn into seam in successive workpieces is varied, resulting in a product of poor appearance.
In addition, because a length of thread chain sewn into seam in a workpiece depends on a cutting point of a cutting device provided in an opening of a suction tube, it has been a problem that a length of thread chain sewn into seam cannot be changed according to products, and some products may have a poorer appearance.